1. Field of the Invention
The present invention relates to the manufacture of skis utilized in winter sports which are adapted to slide on snow and ice.
2. Description of Background and Relevant Information
Conventional skis generally have a composite structure in which there are combined different materials in a manner such that each of them cooperates in an optimal fashion, taking into account the distribution of mechanical stresses. Thus, the structure generally comprises peripheral protection elements forming the upper and lateral surfaces of the ski, internal resistance elements or resistance plates, comprising a material having a high mechanical resistance and high rigidity. The structure likewise comprises filling elements such as a core of a honeycomb structure, a sliding sole forming the lower surface of the ski and assuring good sliding on the snow, and metallic edges forming the lower corners of the ski.
To obtain the appropriate physical characteristics, the manufacture of modern skis relies upon very diverse materials: sliding soles are generally made out of polyethylene; the honeycomb cores are made out of synthetic foam; the edges are made out of steel; the upper surfaces of the ski are formed out of thermoplastic sheets; the resistance elements are made from metal or fiber reinforced resin.
A ski is subjected to severe mechanical stresses requiring good adherence between the various materials constituting the structure.
In traditional techniques of manufacturing skis by injection one positions within the interior cavity of a mold, between the peripheral walls of the cavity, the peripheral elements of the ski, comprising the upper and lower elements of the ski, and, if necessary, lateral elements. One then injects in the space thus defined by the internal surfaces of the peripheral elements, the constituents of a hardenable foam such as a polyurethane foam or a phenolic foam. After expansion and hardening, the foam assures the assembly of the elements.
One of the substantial difficulties in the process of forming skis by injection resides in the positioning and the maintenance of the peripheral elements of the ski before injection. In particular, one must maintain in place before injection of the foam upper and/or lower mechanical reinforcement fabricated materials of the ski, elements formed out of fibers pre-impregnated with a resin. The fabricated materials must then be preliminarily affixed to the peripheral walls of the ski during a preliminary step or be maintained against the walls, without which the foam may penetrate between the fabricated materials and the wall, and create defects in the structure. The maintenance of the fabricated materials requires providing molds of a particular shape comprising lateral cutouts in which there can be positioned the lateral ends of the fabricated materials. The maintenance of the fabricated materials is not possible in the case where the fabricated materials must be pressed to the bottom of a shell having an inverted U shape, the lateral edges of the fabricated materials not being accessible because they are enclosed by the lateral arms of the U.
During its expansion the foam, is capable of pressing the reinforcement elements against the peripheral walls of the ski. However, this pressing is not generally sufficient and, in the case of fabricated materials made out of pre-impregnated fibrous material, the foam tends to infiltrate between the fibers, while poorly pushing the fabricated materials against the walls. As a result there are defects in adherence between the elements, and a substantial deterioration of the mechanical qualities of the mechanical reinforcement element is thus obtained.
Another difficulty resides in the fact that the hardenable foams have mediocre adherence properties for adhering with a certain number of materials adapted to constitute the structure of the ski, or have certain incompatibilities with these materials. As a result, there are defects in adherence between the core made of hardened foam and the other materials of the ski.